1. Field of the Invention
The present invention relates to a liquid discharge head in which desired liquid is discharged by generation of a bubble created by acting thermal energy on liquid, a method for manufacturing such a liquid discharge head, a head cartridge on which such a liquid discharge head is mounted, and a liquid discharge apparatus. More particularly, the present invention relates to a liquid discharge head having a movable member displaced by utilizing generation of a bubble, a method for manufacturing such a liquid discharge head, a head cartridge on which such a liquid discharge head is mounted, and a liquid discharge apparatus.
Incidentally, a term (xe2x80x9crecordingxe2x80x9d in the specification means that not only an image such as a character or a figure having a special meaning but also a meaningless image such as a pattern are formed on a recording medium.
2. Related Background Art
In the past, it is known to propose an ink jet recording method, i.e., so-called bubble jet recording method in which change in state of ink including abrupt volume change (generation of a bubble) is caused by applying energy such as heat to ink, and the ink is discharged from a discharge port by an acting force based on such change of state, thereby effecting recording by adhering the ink onto a recording medium. As disclosed in Japanese Patent Publication No. 61-59911, Japanese Patent Publication No. 61-59914 and U.S. Pat. No. 4,723,129, a recording apparatus using such a bubble jet recording method generally includes discharge ports from which the ink is discharged, ink flow paths communicated with the discharge ports, and heat generating bodies (electrical/thermal converters) as energy generating means disposed within the ink flow paths and adapted to generate energy for discharging the ink.
According to such a recording method, a high quality image can be recorded with low noise and at a high speed. Further, in a head for effecting the recording by using such a recording method, since the discharge ports for discharging the ink can be arranged with high density relatively easily, it is relatively easy to permit formation of an image having high resolving power and a color image by using a compact recording apparatus. As such, the bubble jet recording method has various excellent advantages. Thus, recently, the bubble jet recording method has been applied to various office equipments such as printers, copying machines and facsimiles and also has been applied to industrial equipments such as print apparatuses.
As the bubble jet technique has been utilized in various fields in this way, the following various requests have been increased.
In order to obtain a high quality image, there has been proposed a driving condition for providing a liquid discharging method capable of discharging the ink effectively on the basis of stable bubble generation and high speed ink discharging, or, in the viewpoint of high speed recording, there has been proposed an improved flow path arrangement for providing a liquid discharge head in which a speed of filling (re-fill) of liquid into the flow path to compensate for the discharged liquid is increased.
Other than such a head, in consideration of a back wave (pressure directing toward a direction opposite to a direction toward the discharge port) caused by generation of the bubble, Japanese Patent Application Laid-Open No. 6-31918 discloses a structure in which the back wave giving energy loss in the discharging is prevented. In this structure, a triangular portion of a triangular plate member is disposed in a confronting relationship to a heater for generating the bubble. In this structure, the back wave can slightly be suppressed temporarily by the plate member. However, since there is no teaching and no consideration regarding a relationship between growth of the bubble and the triangular portion, the above-mentioned structure arises the following problem.
That is to say, in the above-mentioned structure, since the heater is disposed on a bottom of a recessed portion not to be linearly communicated with the discharge port, a shape of a liquid droplet cannot be stabilized, and, since the growth of the bubble is permitted from periphery of an apex of the triangle, the bubble is grown throughout from one side of the triangular plate member to the other side thereof, with the result that the growth of the normal bubble is completed as if there is no plate member. Accordingly, the grown bubble does not relates to the presence of the plate member. Rather, since the entire plate member is surrounded by the bubble, during contraction of the bubble, the re-fill to the heater disposed in the recessed portion causes a turbulent flow, which may accumulates small bubbles in the recessed portion, thereby deteriorating the principle itself for discharging the ink based on the growth of the bubble.
Further, European Patent Publication No. 0 436 047 A1 proposes the invention in which a first valve disposed between an area near a discharge port and a bubble generating area and adapted to block these areas and a second valve disposed between the bubble generating area and an ink supplying area and adapted to completely block these areas are alternately opened and closed (refer to FIGS. 4 to 9 of this document). However, in this invention, since three chambers are divided into groups (two chambers), in the discharging, the ink following to a liquid droplet has a long tail, with the result that many satellite dots are created in comparison with the normal discharging system including growth, contraction and disappearance of the bubble (It is guessed that effect of retraction of meniscus due to disappearance of the bubble cannot be utilized). Further, in the re-fill, although the liquid is supplied to the bubble generating area as the disappearance of the bubble, since the liquid cannot be supplied to the area near the discharge port until the next bubble is generated, not only there is great dispersion in discharged liquid droplets, but also discharge response frequency becomes very small, and, thus, this invention cannot be put to a practical use.
In consideration of the fundamental liquid discharging principle, the inventors investigated to provide a new liquid discharging method utilizing a bubble and a head used therewith, which were not obtained in the past, and proposed the invention using a movable member (plate member having a free end positioned near a discharge port with respect to a fulcrum) effectively contributing to the discharging of liquid, which is different from the conventional techniques (for example, refer to Japanese Patent Application Laid-Open No. 9-201966).
Now, the liquid discharging method and the head used therewith, as disclosed in the Japanese Patent Application Laid-Open No. 9-201966 will be described with reference to FIGS. 29A to 29D and FIG. 30. FIGS. 29A to 29D are sectional views of a liquid discharge head, taken along a liquid flow path, explaining the discharging principle. FIG. 30 is a partial sectional perspective view of the liquid discharge head shown in FIGS. 29A to 29D. The liquid discharge head shown in FIGS. 29A to 29D and FIG. 30 has a most fundamental arrangement for realizing the liquid discharging method disclosed in the Japanese Patent Application Laid-Open No. 9-201966 to improve a discharging force and discharging efficiency by controlling a growing direction of a bubble and a propagating direction of pressure created by generation of the bubble in the liquid discharging.
Incidentally, in this specification, terms xe2x80x9cupstreamxe2x80x9d and xe2x80x9cdownstreamxe2x80x9d are used with respect to a direction of the liquid flowing from a liquid supplying source through above a bubble generating area (or movable member) toward a discharge port.
The term xe2x80x9cdownstream sidexe2x80x9d regarding the bubble itself means a discharge port side portion of the bubble mainly relating to the discharging of a liquid droplet directly. More specifically, xe2x80x9cdownstream sidexe2x80x9d means a downstream side of the center of the bubble or a downstream side of the center of an area of a heat generating member, with respect to the flowing direction.
Further, xe2x80x9ccomb toothxe2x80x9d is a term used with respect to the movable member and means a configuration in which a connecting part to a base is a common portion from which a plurality of movable portion are branched toward a free end which is opened outwardly.
In the example shown in FIGS. 29A to 29D, the liquid discharge head includes a heat generating member 1102 (heat generating resistor having a dimension of 20 xcexcmxc3x97105 xcexcm in this example) for acting thermal energy on liquid, as a discharge energy generating element adapted to generate discharge energy for discharging the liquid and disposed on an element substrate 1101, and a liquid flow path 1103 is formed above the element substrate 1101 in correspondence to the heat generating member 1102. The liquid flow path 1103 is communicated with a discharge port 1104. The plurality of liquid flow paths 1103 are communicated with a common liquid chamber 1105 for supplying the liquid to the plurality of liquid flow paths. After the liquid is discharged from the discharge port 1104, an amount of liquid corresponding to the discharge liquid is supplied from the common liquid chamber 1105 to the liquid flow path 1103.
Within the liquid flow path 1103, above the element substrate 1101, a plate-shaped movable member 1106 made of elastic material such as metal and having a flat surface portion opposed to the heat generating member 1102 is supported in a cantilever fashion. One end of the movable member 1106 is secured to a base (support member) 1107 formed by patterning photosensitive resin on a wall of the liquid flow path 1103 or the element substrate 1101, thereby providing a fulcrum (fixed end) 1108.
Further, the movable member 1106 has a comb shape. In this way, the movable member 1106 can easily be manufactured with a low cost, and alignment of the movable member with respect to the base can be facilitated.
The movable member 1106 is arranged in a confronting relation to and spaced apart from the heat generating member 1102 by about 15 xcexcm to cover the heat generating member in such a manner that the fulcrum 1108 is disposed at an upstream side of great liquid flow flowing from the common liquid chamber 1105 through above the movable member 1106 toward the discharge port 1104 during the liquid discharging operation and a free end 1109 is disposed at a downstream side of the fulcrum 1108. A bubble generating area 1110 is defined between the heat generating member 1102 and the movable member 1106.
By heating the heat generating member 1102, heat is applied to the liquid in the bubble generating area 1110 between the movable member 1106 and the heat generating member 1102, with the result that a bubble 1111 is generated in the liquid in accordance with a film-boiling phenomenon as disclosed in U.S. Pat. No. 4,723,129 (refer to FIG. 29B). Pressure caused by generation of the bubble 1111 preferentially acts on the movable member 1106, with the result that, as shown in FIGS. 29B and 29C, the movable member 1106 is displaced to be opened greatly toward the discharge port 1104 around the fulcrum 1108. When the movable member 1106 is displaced, propagation of the pressure created by the generation of the bubble and growth of the bubble are directed toward the discharge port 1104. Further, in this case, since a width of the free end 1109 is relatively wide, a bubbling power of the bubble 1111 can easily be directed toward the discharge port 1104, thereby fundamentally enhancing liquid discharging efficiency and discharging speed. In FIGS. 29B and 29D, C indicates a center of an area of the heat generating member and L indicates the liquid.
As mentioned above, in the technique disclosed in the Japanese Patent Application Laid-Open No. 9-201966, by arranging the free end 1109 of the movable member 1106 at the downstream side, i.e., toward the discharge port 1104 and by opposing the movable member 1106 to the heat generating member 1102 and the bubble generating are 1110, the bubble 1111 is controlled positively.
Further, as mentioned above, by securing the movable member 1106 to the base 1107, a gap of about 1 to 20 xcexcm is created between the movable member 1106 and the heat generating member 1102, thereby enhancing the liquid discharging efficiency of the movable member 1106 considerably. Accordingly, according to the liquid discharge head based on the new discharging principle as mentioned above, since a combined effect of the generated bubble 1111 and the displaced movable member 1106 can be obtained and since the liquid in the vicinity of the discharge port 1104 can be discharged efficiently, the liquid discharging efficiency can be enhanced in comparison with the conventional bubble jet liquid discharge heads.
Incidentally, although various materials can be used to manufacture the movable member 1106 used in the above-mentioned liquid discharge head, nickel having excellent elasticity is generally used for efficiently utilizing the pressure created by the generation of the bubble 1111. Further, as disclosed in Japanese Patent Application Laid-Open Nos. 11-170531 and 11-235829, materials of silicon group are generally used.
Further, Japanese Patent Application Laid-Open No. 9-48127 discloses the invention in which an upper limit of the displacement of the movable member is regulated in order to prevent distortion of performance of the movable member. Further, Japanese Patent Application Laid-Open No. 9-323420 discloses the invention in which the position of the upstream common liquid chamber is shifted toward the free end of the movable member, i.e., toward a downstream side with respect to the movable member to utilize the advantage of the movable member thereby to enhance the re-filling ability. In these inventions, since it is assumed that the growth of the bubble is released at once toward the discharge port from the condition that the bubble is temporarily entrapped by the movable member, individual elements relating to the formation of liquid droplet by means of the bubble and relationships therebetween were not noticed.
As a next step, Japanese Patent Application Laid-Open No. 10-24588 discloses the invention in which a part of the bubble generating area is released from the movable member, as an invention in which the growth of the bubble due to propagation of pressure wave (acoustic wave) is noticed as a factor relating to the liquid discharging. However, also in this invention, since only the growth of the bubble during the liquid discharging is noticed, individual elements relating to the formation of liquid droplet by means of the bubble and relationships therebetween were not noticed.
Although the fact that a forward portion of the bubble generated by the film-boiling affects a great influence upon the discharging (edge-shooter type) is well-known, in the past, a technique in which such a forward portion is contributed to formation of the discharge liquid droplet more efficiently has not been noticed. The inventors have investigated technical analysis regarding such a technique.
Further, the inventors obtained the following effective knowledge by checking the displacement of the movable member and the generated bubble.
Such knowledge is to regulate displacement of the free end of the movable member with respect to the growth of the bubble by means of a regulating portion (stopper). By regulating the displacement of the movable member by means of the regulating portion, the bubble is regulated to be grown toward the upstream side of the flow path, with the result that energy for discharging the liquid can be transferred to the downstream side where the discharge port is formed.
As high density arrangement of the head has been progressed, in the viewpoint of accuracy, it becomes considerably difficult to manufacture the movable member and the base independently and to realize alignment therebetween, and, thus, it has been requested that the movable member and the base be integrally formed.
If the movable member including the base (fixing portion) is formed in this way, the movable member has a stepped structure between the base and a movable part. If the movable member has a portion a configuration of which is greatly changed in this way, during the displacement of the movable member caused by the generation of the bubble, stress may be concentrated into such a portion. Further, the movable member is branched to form the comb configuration as mentioned above and root portions of the comb configuration are also greatly deformed to concentrate stress therein. Particularly, if the comb-branched plural movable parts are displaced simultaneously, excessive stress may act on the boundary portion between the movable parts and the base.
Although the above-mentioned material of silicon group preferably used for manufacturing the movable member is flexible material having excellent elasticity, if excessive stress acts on such material, crack may generated in the material to worsen endurance of the movable member. If the crack is generated, the stress is further concentrated into the cracked area thereby to break the movable member ultimately. Further, when the metallic material is used, if the excessive stress acts on the material, undesirable influence may occur. Normally, the movable member has adequate endurance by increasing a thickness of the material not to arise any problem if some stress acts thereon.
However, if the movable member of the liquid discharge head is formed as a film from metal such as nickel by spattering, it is difficult to control the stress, and it is difficult to increase the film thickness. Further, when the movable member is formed from material of silicon group by a CVD method, although the stress can be controlled and the film thickness of the movable member integral with the base can be increased, also in this case, if the excessive stress acts, the endurance of the movable member will be worsened.
Further, in the liquid discharge head having the movable member, whenever the liquid is discharged, the displacement and restoring of the movable member are repeated as the liquid is heated and generation and disappearance of the bubble occur. However, if a bubble greater than the bubble normally used for discharging the liquid is generated, the movable member may be deformed excessively. Normally, although the flow path is filled with the liquid except for a meniscus portion at the discharge port, after suction recovery processing of the liquid discharge head is performed, if the excessive liquid is removed, a space which is not filled with the liquid may be generated within the flow path. In such a condition, when the heat generating member is heated to discharge the liquid, the movable member is displaced due to the bubbling of the liquid, with the result that the free end (distal end) of the movable member is regulated by the regulating portion to be stopped at a desired position. However, an intermediate portion of the movable member (portion between the free end and the fulcrum) is not regulated and is strongly pulled upwardly. Particularly, in a condition that the space which is not filled with the liquid exists above the movable member, since there is no pressure of the liquid, the movable member is subjected to great stress for pulling the movable member toward the upstream side, with the result that convex flexure directed upwardly (toward a top plate) is created. Due to such flexure deformation, crack or defect may be generated in the movable member. Further, if the flexure deformation is increased or is repeated frequently, the movable member may be broken.
The present invention is made in consideration of the above-mentioned conventional drawbacks, and an object of the present invention is to provide a liquid discharge head in which endurance of stepped portions of a movable member and of root portions of movable parts of the movable member can be enhanced and reliability of liquid discharging can be enhanced, a method for manufacturing such a liquid discharge head, a head cartridge on which such a liquid discharge head is mounted, and a liquid discharge apparatus.
Another object of the present invention is to provide a liquid discharge head and a liquid discharge apparatus, in which endurance of a movable member is enhanced and a discharging property is stabilized by not only regulating displacement of a free end of the movable member but also preventing flexure deformation and which have high reliability.
To achieve the above objects, the present invention provides a liquid discharge head which comprises a discharge port for discharging liquid, a liquid flow path communicated with the discharge port and adapted to supply the liquid to the discharge port, an element substrate including a heat generating member for generating a bubble in the liquid filled in the liquid flow path, a movable member having a fixed portion supported by and secured to the element substrate, and a free end positioned toward the discharge port and movable parts disposed at a position opposed to the heat generating member on the element substrate and spaced apart from the element substrate by a gap therebetween, and a regulating portion for regulating a displacement amount of the movable member, and in which the liquid is discharged from the discharge port by pressure created by generation of a bubble meanwhile the movable part of the movable member is displaced, wherein the regulating portion comprises a distal end regulating part abutting against the free end of the movable member and at least one displacement regulating part spaced apart from the distal end regulating part.
The movable member is constituted by integrally forming the fixed portion, plurality of movable parts and a common support portion spaced apart from the element substrate and adapted to branch and support the movable parts so that, when the liquid is discharged, the movable part is displaced around a connection portion between the movable part and the common support portion as a fulcrum, and the displacement regulating part may be an auxiliary member which is provided in an opposed relationship to at least common support portion of the movable member to suppress excessive displacement of the common support portion.
With the above-mentioned arrangement, the stress (which acts on the connection portion between the common support portion and the fixed portion and on the root portions of the branched movable parts and which can be concentrated during the displacement of the movable member if there is no auxiliary member) can be dispersed into the auxiliary member and be relaxed.
When the auxiliary member is opposed to the common support portion to suppress the excessive displacement of the common support member, although an effect for relaxing the stress acting on the movable member can be obtained, by providing the auxiliary member to abut against at least an upper surface of the movable member, a function for relaxing the stress can be obtained more effectively. Further, by providing the auxiliary member to extend onto and abut against the element substrate between the plural branched movable parts, a portion of the movable member into which the stress is apt to be concentrated can be firmly supported, thereby relaxing the stress more effectively. In order to obtain the function for relaxing the stress concentration more effectively, it is desirable that the auxiliary member be formed to extend into the space between the movable parts of the movable member and the element substrate, i.e., to cover the entire root portions of the movable parts.
Further, when the auxiliary member is formed along a direction along which the branched movable parts are arranged side by side, the stress acting on the movable parts can be dispersed in such a direction and be relaxed uniformly between the movable parts, thereby enhancing endurance of the branched movable parts.
Further, the auxiliary member may be formed integrally with flow path walls forming side walls of the liquid flow path. In this case, the auxiliary member can be formed without increasing the number of manufacturing steps.
Material for the auxiliary member may be photosensitive resin, particularly, resin of epoxy group.
In the above-mentioned method for manufacturing the liquid discharge head of the present invention, when the flow path walls and the auxiliary member are formed simultaneously from the same material, the auxiliary member can easily be formed without increasing the number of manufacturing steps. In this case, a manufacturing method including a step for forming the movable member on the element substrate, a step for pouring liquid-state photo-curable resin into the gap between the movable member and the element substrate and coating such resin on the element substrate until the movable member is covered, a step for curing the photo-curable resin by exposure at least in areas where the flow path walls and the auxiliary member are to be formed, and a step for removing uncured photo-curable resin can preferably be used.
Further, the flow path walls and the auxiliary member may be formed independently in consideration of respective functions. In this case, a manufacturing method including a step for forming the movable member and the flow path walls defining the side walls of the flow path on the element substrate, a step for pouring liquid-state photo-curable resin into the gap between the movable member and the element substrate and coating such resin on the element substrate until the movable member is covered, a step for curing the photo-curable resin by exposure at least in areas where the auxiliary member is to be formed, and a step for removing uncured photo-curable resin can preferably be used.
As mentioned above, when the auxiliary member is formed from negative type photo-curable resin which can be cured by exposure, by forming the movable member from transparent material, since the gap between the movable member and the element substrate can also be exposed, the auxiliary member can be formed in the gap.
Further, according to another liquid discharge head of the present invention, the displacement regulating portion is constituted by at least one flexure regulating portion spaced apart from the distal end regulating portion and disposed at an upstream side of the heat generating member and capable of abutting against the intermediate portion of the movable member. The flexure regulating portion may abut against the intermediate portion of the movable member only when the movable member is displaced excessively.
With this arrangement, since the displacement of the free end of the movable member is regulated by the distal end regulating portion and the flexure displacement of the intermediate portion of the movable member is regulated by the flexure regulating portion, the movable member is not displaced excessively. Accordingly, crack and/or defect is not created in the movable member, thereby preventing the movable member from being broken.
It is preferable that the distal end regulating portion and the flexure regulating portion are formed independently on the top plate joined to the element substrate.
Preferably, a sectional area of the distal end regulating portion in a direction perpendicular to a liquid flowing direction in the liquid flow path is greater than a sectional area of the flexure regulating portion in the direction perpendicular to the liquid flowing direction in the liquid flow path. In this case, the distal end regulating portion may have a width wider than that of the flexure regulating portion. With this arrangement, the excessive displacement of the movable member is prevented and a re-fill property is not worsened. Further, a plurality of distal end regulating portions may be provided.
A head cartridge according to the present invention is characterized in that it comprises the above-mentioned liquid discharge head, and a liquid container for storing the liquid to be supplied to the liquid discharge head.
A liquid discharge apparatus according to the present invention is characterized in that it comprises the above-mentioned liquid discharge head, and drive signal supplying means for supplying a drive signal for discharging the liquid from the discharge port. Further, conveying means for conveying a recording medium for receiving the liquid discharged from the liquid discharge head may be provided.
Incidentally, in the explanation of this invention, terms xe2x80x9cupstreamxe2x80x9d and xe2x80x9cdownstreamxe2x80x9d are used with respect to a direction of the liquid flowing from a liquid supplying source through above the bubble generating area (or movable member) toward the discharge port and with respect to the constructural direction.
Further, the term xe2x80x9cdownstream sidexe2x80x9d regarding the bubble itself means a bubble generated in an area at a downstream side as for the flowing direction or the constructural direction with respect to the center of the bubble or at a downstream side of the center of the area of the heat generating body. Similarly, the term xe2x80x9cupstream sidexe2x80x9d regarding the bubble itself means a bubble generated in an area at an upstream side as for the flowing direction or the constructural direction with respect to the center of the bubble or at an upstream side of the center of the area of the heat generating body.